NEW YORK (AP) _ Merck & Co., the giant pharmaceutical concern, has topped the list of Fortune magazine's most admired U.S. companies for the second consecutive year.

The Rahway, N.J.-based company scored the highest overall rating ever in the six years the survey has been conducted. The results, which were released on Wednesday, are in the Jan. 18 issue of Fortune that appears on newstands Monday.

Ranked second was the rubber products company Rubbermaid Inc., based in Wooster, Ohio, up from fifth place a year ago.

Third was Dow Jones & Co., the New York-based publisher of The Wall Street Journal and other financial publications, up from ninth a year ago.

Procter & Gamble Co., the consumer products giant based in Cincinnati, ranked fourth, up from 18th a year ago, and Liz Claiborne Inc., the clothing maker, finished fifth, down from second a year ago.

Next were Minnesota Mining & Manufacturing Co., the scientific and photographic equipment company based in St. Paul, Minn.; Philip Morris Companies Inc., the tobacco, food and beverage company based New York; and J.P. Morgan & Co., the New York-based commercial banker.

Tied for ninth place were newcomers to the Top 10: RJR Nabisco Inc., the tobacco and foods company based in Winston-Salem, N.C., and Wal-Mart Stores Inc., a retailer based in Bentonville, Ark.

International Business Machines Corp., the computer giant from Armonk, N.Y., which ranked as the most admired company in each of the first four Fortune surveys, slipped out of the Top 10 listing for the first time, falling to 32nd place from the seventh spot last year.

The least admired company of the 306 in the survey was Financial Corp. of America, based in Irvine, Calif., and operator of the nation's largest savings and loan. FCA has taken heavy loan-loss provisions in recent years.

The rankings are based on 3,480 replies to a survey of more than 8,000 top executives, outside directors and financial analysts. Ninety percent of the returns were in hand before the Oct. 19 stock crash, but Fortune said the final 10 percent showed no effects from the market's collapse.

Those surveyed were asked to rate the 10 largest companies in their own industries on eight key attributes, including quality of management, quality of products or services, innovativeness, long-term investment value, financial soundness, community and environmental responsibility, use of corporate assets and ability to attract and keep talented people.

Ratings were on a scale of zero to 10 with 10 being the best mark, and included 33 industries with assignments being made according to the business that contributed the most to a company's 1986 sales.

Merck ranked first according to each of the eight attributes but one - community and environmental responsibility in which Johnson & Johnson, a pharmaceutical and medical products company based in New Brunswick, N.J., was ranked first.

Merck expects its 1987 profits will rise 30 percent on a 20 percent sales increase amid strong demand for its cardiovascular drugs and antibiotics. It also rolled out a cholesterol fighter called Mevacor in September.

The second least admired company was American Motors Corp., based in Southfield, Mich. It was recently acquired by rival automaker Chrysler Corp.

Others in the bottom five, listed in ascending order, were BankAmerica Corp., the commercial banking firm based in San Franciso; LTV Corp., the metals company based in Dallas; and Bethlehem Steel Corp., another metals maker based in Betlehem, Pa.

The company taking the biggest tumble in the rankings was Allegis, the Chicago-based parent of United Airlines. It fell to 290th place, from 188th a year ago.